Combination Photodetector Arrays for Extended Dynamic Range

ABSTRACT

The present disclosure relates to methods and systems that improve the dynamic range of LIDAR systems. An example system includes a plurality of single-photon photodetectors and at least one additional photodetector monolithically integrated on a shared substrate. The plurality of single-photon photodetectors and the at least one additional photodetector are configured to detect light from a shared field of view. The system also includes a controller configured to carry out operations. The operations include: receiving respective photodetector signals from the plurality of single-photon photodetectors and the at least one additional photodetector; selecting a photodetector signal from at least two of: the two received photodetector signals and a combined photodetector signal formed by combining the two received photodetector signals; and determining an intensity of light in the field of view based on the selected photodetector signal.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Light detection and ranging (LIDAR) devices may estimate distances toobjects in a given environment. For example, an emitter subsystem of aLIDAR system may emit near-infrared light pulses, which may interactwith objects in the system's environment. At least a portion of thelight pulses may be redirected back toward the LIDAR (e.g., due toreflection or scattering) and detected by a receiver subsystem.Conventional receiver subsystems may include a plurality of detectorsand a corresponding controller configured to determine an arrival timeof the respective light pulses with high temporal resolution (e.g., ˜400ps). The distance between the LIDAR system and a given object may bedetermined based on a time of flight of the corresponding light pulsesthat interact with the given object.

SUMMARY

The present disclosure relates to methods and systems that improve thedynamic range of LIDAR systems. For example, a receiver subsystem of aLIDAR system may utilize inputs from different types of photodetectorsso as to provide a higher dynamic range LIDAR imaging capability.

In a first aspect, a system is provided. The system includes asubstrate, a plurality of single-photon photodetectors coupled to thesubstrate, and at least one additional photodetector coupled to thesubstrate. The single-photon photodetectors and the at least oneadditional photodetector are arranged to detect light from a field ofview. The at least one additional photodetector is other than asingle-photon photodetector. The system also includes a controllerconfigured to execute program instructions so as to carry outoperations. The operations include receiving a first photodetectorsignal from the plurality of single-photon photodetectors. The firstphotodetector signal is indicative of light from the field of viewdetected by the single-photon photodetectors. The operations alsoinclude receiving a second photodetector signal from the at least oneadditional photodetector. The second photodetector signal is indicativeof light from the field of view detected by the at least one additionalphotodetector. The operations additionally include selecting aphotodetector signal from at least two of: the first photodetectorsignal, the second photodetector signal, and a combined photodetectorsignal formed by combining the first and second photodetector signals.The operations yet further include determining an intensity of light inthe field of view based on the selected photodetector signal.

In a second aspect, a method is provided. The method includes receivinga first photodetector signal from a plurality of single-photonphotodetectors. The first photodetector signal is indicative of lightfrom a field of view detected by the single-photon photodetectors. Themethod also includes receiving a second photodetector signal from atleast one additional photodetector. The second photodetector signal isindicative of light from the field of view detected by the at least oneadditional photodetector. The at least one additional photodetector isother than a single-photon photodetector. The plurality of single-photonphotodetectors and the at least one additional photodetector are coupledto a substrate. The method additionally includes selecting aphotodetector signal from at least two of: the first photodetectorsignal, the second photodetector signal, and a combined photodetectorsignal formed by combining the first and second photodetector signals.The method yet further includes determining an intensity of light in thefield of view based on the selected photodetector signal.

Other aspects, embodiments, and implementations will become apparent tothose of ordinary skill in the art by reading the following detaileddescription, with reference where appropriate to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A illustrates a system, according to an example embodiment.

FIG. 1B illustrates a system, according to an example embodiment.

FIG. 1C illustrates a scenario, according to an example embodiment.

FIG. 2A illustrates a system, according to an example embodiment.

FIG. 2B illustrates a system, according to an example embodiment.

FIG. 3 illustrates a circuit, according to an example embodiment.

FIG. 4 illustrates a method, according to an example embodiment.

DETAILED DESCRIPTION

Example methods, devices, and systems are described herein. It should beunderstood that the words “example” and “exemplary” are used herein tomean “serving as an example, instance, or illustration.” Any embodimentor feature described herein as being an “example” or “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments or features. Other embodiments can be utilized, and otherchanges can be made, without departing from the scope of the subjectmatter presented herein.

Thus, the example embodiments described herein are not meant to belimiting. Aspects of the present disclosure, as generally describedherein, and illustrated in the figures, can be arranged, substituted,combined, separated, and designed in a wide variety of differentconfigurations, all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall embodiments, with the understanding that not allillustrated features are necessary for each embodiment.

I. Overview

While operated in Geiger mode, silicon photomultiplier detectors(SiPMs), single photon avalanche diodes (SPADs), or other types ofsensitive photodetectors can provide single photon-level sensing,however such devices generally provide a relatively low dynamic range(e.g., 0-3000 photons). As an example, SiPMs may become saturated inscenarios with relatively high light levels (e.g., retroreflection,close range objects, etc.).

In contrast, linear mode avalanche photodiodes (LmAPDs) provide a higherdynamic range, but are not able to detect light at the single photonlevel. That is, LmAPDs lack extremely low light detection capability.

Embodiments include systems and methods involving a combination ofdifferent photodetectors (e.g., SiPMs and LmAPDs) having differentrespective photosensitivity, spectral responsivity, and/or dynamic rangeattributes. Such detector combinations may provide low light detectionas well as high dynamic range at high light levels (e.g., scenes withretroreflections, close range objects, etc.). Example embodimentsinclude a combination of APDs and SiPMs integrated in a monolithicmanner. That is, the APDs and SiPMs may be collocated on the same boardand/or even the same substrate. As an example embodiment, APD devicescould be fabricated on the same substrate as a SiPM detector array usingone or two additional photolithography mask fabrication steps.

Output signals (e.g., photosignals) from a plurality of detectors of afirst detector type (e.g., SiPMs) may be routed to a first input channelon a microcontroller or logic unit. Similarly, output signals from aplurality of detectors of a second detector type (e.g., APDs) may berouted to a second input channel of the microcontroller or logic unit.In low light situations, the logic unit may select the SiPM signal asbeing representative of the actual light intensity and ignore the noisyor non-linear APD signal. In bright light scenarios, the logic unit mayselect the APD signal as being representative of the actual lightintensity and ignore the saturated SiPM signal. In other light levelscenarios, the respective signals from the APD and SiPM may be mixed orweighted in varying proportions to provide a substantially linear signalintensity versus photons detected.

In another embodiment, pairs of APDs and SiPMs could be arranged in aparallel circuit. In some embodiments, such paired detectors may becoupled using a pole zero network. In such a scenario, the currentthrough the parallel combination could provide an analog signalindicative of the actual light level.

In an alternative embodiment, PIN diodes could be used instead of, or inaddition to the APDs. That is, in some embodiments, imaging systems mayincorporate more than two types of detectors (e.g., SiPM, APD, PINdiode, bolometer, photoconductor, etc.). In other embodiments, the APDdevices could be stacked underneath corresponding SiPM devices. In sucha scenario, photons that are not absorbed by the SiPM devices may betransmitted through the SiPM (and possibly interposing materials) to theAPD devices. In such a manner, both low light levels and bright lightlevels could be detected.

II. Example Systems

FIG. 1A illustrates a system 100, according to an example embodiment.The system 100 includes a plurality of single-photon photodetectors 110that is coupled to a substrate 102. The plurality of single-photonphotodetectors 110 includes a plurality of photodetectors of a firstphotodetector type 112.

The system 100 also includes at least one additional photodetector 120that is coupled to the substrate 102. The at least one additionalphotodetector 120 includes one or more photodetectors of a secondphotodetector type 122. That is, the at least one additionalphotodetector is a photodetector that is not a single-photonphotodetector. In some embodiments, the first photodetector typeincludes a silicon photomultiplier (SiPM) detector. Example embodimentsmay include the second photodetector type as being at least one of: anavalanche photodiode (APD) detector or a PIN photodiode detector. Otherphotodetector types are also possible and contemplated herein.

In some embodiments, the substrate 102 may include a first surface. Insuch scenarios, the first surface could be disposed along a primaryplane of the substrate 102.

The plurality of single-photon photodetectors 110 and the at least oneadditional photodetector 120 could be coupled to the first surface. Forexample, the plurality of single-photon photodetectors 110 and the atleast one additional photodetector 120 could be disposed in aside-by-side arrangement on the same surface of the substrate 102.

In another embodiment, at least a portion of detectors of the pluralityof single-photon photodetectors 110 could be arranged along the firstsurface among at least a portion of detectors of the at least oneadditional photodetector 120 so as to form an intermingled photodetectorarrangement. In other embodiments, the plurality of single-photonphotodetectors 110 and the at least one additional photodetector 120could be disposed in other arrangements and/or coupled to differentsurfaces of the substrate 102.

Other arrangements of the plurality of single-photon photodetectors 110and the at least one additional photodetector 120 are possible. Forexample, the plurality of single-photon photodetectors 110 could becoupled to an upper surface of the at least one additional photodetector120 so as to form a stacked photodetector arrangement.

Yet further, while examples described herein relate to the substrate102, it will be understood that other embodiments could include therespective detectors arranged on two or more substrates. For instance,the plurality of single photon photodetectors 110 could be arrangedalong a surface of a first substrate and the at least one additionalphotodetector 120 could be arranged along a surface of a secondsubstrate. Other detector arrangements that include more than onesubstrate are possible and contemplated herein.

In some embodiments, the plurality of single-photon photodetectors 110are arranged to detect light from a field of view. In such scenarios,the at least one additional photodetector 120 is arranged to detectlight from at least a portion of the same field of view. In an exampleembodiment, the system 100 includes imaging optics 142. In suchscenarios, the plurality of single-photon photodetectors 110 and the atleast one additional photodetector 120 may both detect light from theshared field of view by way of the imaging optics 142.

In some embodiments, the system 100 includes photodetector outputcircuitry 128. The plurality of single-photon photodetectors 110 and theat least one additional photodetector 120 may be coupled to thephotodetector output circuitry 128.

The system 100 also includes a logic unit 130. In an example embodiment,the logic unit 130 includes a first input channel 132 and a second inputchannel 134. In such a scenario, respective photodetector signals of theplurality of single-photon photodetectors 110 are routed to a firstinput channel 132 of the logic unit 130. The respective photodetectorsignals of the at least one additional photodetector 120 are routed to asecond input channel 134 of the logic unit 130.

In an example embodiment, while in a low light situation, the logic unit130 may select the SiPM signal as being representative of the actuallight intensity and ignore a noisy or non-linear APD signal. Incontrast, in bright light scenarios, the logic unit 130 may select theLmAPD signal as being representative of the actual light intensity andignore the saturated SiPM signal. In other light level scenarios, therespective signals from the LmAPD and SiPM may be mixed or weighted invarying proportions to provide a substantially linear signal intensityversus photons detected.

In some embodiments, the system 100 includes an exposure meter 140. Theexposure meter 140 may be configured to provide information indicativeof a lighting condition to the logic unit 130. In at least someembodiments, the logic unit 130 may provide a combined image based onthe lighting condition.

In some example embodiments, the system 100 may include a plurality oflight sources 144. The plurality of light sources 144 may includelasers, although other types of light sources are also contemplated.Some embodiments may include the plurality of light sources 144 mayinclude 256 laser light sources. In such scenarios, the plurality ofsingle-photon photodetectors 110 and the at least one additionalphotodetector 120 may each include 256 photodetectors. Other amounts oflight sources and photodetectors are possible and contemplated.

The system 100 additionally includes a controller 150. In someembodiments, controller 150 may include some or all of the functionalityof logic unit 130. The controller 150 includes at least one processor152 and a memory 154. The at least one processor 152 may include, forinstance, an application-specific integrated circuit (ASIC) or afield-programmable gate array (FPGA). Other types of processors,computers, or devices configured to carry out software instructions arecontemplated herein. The memory 154 may include a non-transitorycomputer-readable medium, such as, but not limited to, read-only memory(ROM), programmable read-only memory (PROM), erasable programmableread-only memory (EPROM), electrically erasable programmable read-onlymemory (EEPROM), non-volatile random-access memory (e.g., flash memory),a solid state drive (SSD), a hard disk drive (HDD), a Compact Disc (CD),a Digital Video Disk (DVD), a digital tape, read/write (R/W) CDs, R/WDVDs, etc.

The at least one processor 152 is configured to execute programinstructions stored in the memory 154 so as to carry out operations. Insome embodiments, the operations include receiving a first photodetectorsignal from the plurality of single-photon photodetectors. In someembodiments, the first photodetector signal may be indicative of lightfrom the field of view detected by the single-photon photodetectors.

The operations additionally include receiving a second photodetectorsignal from the at least one additional photodetector. In suchscenarios, the second photodetector signal may be indicative of lightfrom the field of view detected by the at least one additionalphotodetector.

The operations also include selecting a photodetector signal from atleast two of: the first photodetector signal, the second photodetectorsignal, and a combined photodetector signal formed by combining thefirst and second photodetector signals.

Yet further, the operations include determining an intensity of light inthe field of view based on the selected photodetector signal.

In some embodiments, the operations may include receiving informationindicative of an exposure condition of at least a portion of the sharedfield of view. For example, the exposure meter 140 may provideinformation about the exposure condition. In such scenarios, thecombined photodetector signal may be formed by a combination of thefirst and second photodetectors that is based on the exposure condition.

The controller 150 may include a computer disposed on a vehicle, anexternal computer, or a mobile computing platform, such as a smartphone,tablet device, personal computer, wearable device, etc. Additionally oralternatively, the controller 150 may include, or be connected to, aremotely-located computer system, such as a cloud server. In an exampleembodiment, the controller 150 may be configured to carry out some orall method blocks or steps described herein.

In some embodiments, the operations include selecting the photodetectorsignal. Selecting the photodetector signal may include comparing thefirst photodetector signal to a first threshold. The first thresholdcould be a threshold voltage, a threshold current, and/or a rate ofchange of a voltage or current. In response to a determination that thefirst photodetector signal is less than the first threshold, theoperations may include selecting the first photodetector signal as theselected photodetector signal. That is, in some embodiments, if aphotocurrent or photovoltage is below a threshold current or thresholdvoltage, a signal from the single photon detectors may be desirable.That is, at low light levels, the SiPM signals may be the only relevantphotosignals as the APDs or other photodetectors may not be able todetect photons at such low levels.

In some embodiments, the operations may include comparing the secondphotodetector signal to a second threshold. The second threshold couldbe, for example, a threshold voltage or threshold current (or rate ofchange of voltage/current) that could be indicative of a relatively highlight level (e.g., a light level at which APDs may be effective). Insuch a scenario, in response to a determination that the secondphotodetector signal is greater than the second threshold, theoperations may include selecting the second photodetector signal as theselected photodetector signal. That is, at relatively high light levels,the non-single photon detectors could be selected.

In yet further embodiments, selecting the photodetector signal mayinclude comparing the first photodetector signal to a first threshold,comparing the second photodetector signal to a second threshold, and, inresponse to a determination that the first photodetector signal isgreater than the first threshold and the second photodetector signal isless than the second threshold, combining the first and secondphotodetector signals and selecting the combined photodetector signal asthe selected photodetector signal. In other words, if the photon flux isgreater than a minimum threshold photocurrent/photovoltage but less thana maximum photocurrent/photovoltage, the signals from the first andsecond photodetectors could be combined so as to provide a higherdynamic range than if the photodetectors were utilized alone.

Some example embodiments need not include one or more comparisons to athreshold. In such scenarios, an operation could be performed on thefirst and the second photodetector signals so as to combine them. Forexample, combining the first and the second photodetector signals couldinclude taking a weighted sum based on the first and the secondphotodetector signals.

In some embodiments, combining the first and second photodetectorsignals may include adjusting the first photodetector signal. In suchscenarios, adjusting the first photodetector signal may includemultiplying the first photodetector signal by a first value of a highdynamic range profile. Combining the first and second photodetectorsignals may include adjusting the second photodetector signal. In suchscenarios, adjusting the second photodetector signal may includemultiplying the second photodetector signal by a second value of thehigh dynamic range profile. Combining the first and second photodetectorsignals may also include summing the adjusted first and secondphotodetector signals. It will be understood that other ways ofcombining the first and second photodetector signals are contemplatedherein.

In some embodiments, the high dynamic range profile could include a lookup table (LUT). At least some information in the look up table couldinclude values between 0.0 and 1.0. For example, the look up table mayinclude three columns. A first column could include a range of exposureconditions or photon flux levels. A second column could include valuesbetween 0.0 and 1.0 that represent a multiplier for the photosignalsfrom the first detector array 110. A third column could include valuesbetween 1.0 to 0.0 that represent a multiplier for the photosignals fromthe at least one additional photodetector 120. In such scenarios, thelook up table may provide information to appropriately mix therespective photosignals from the first detector array 110 and the atleast one additional photodetector 120 based on a present exposurecondition. Other information, arrangements, and/or values may beincluded in the look up table. As an example, the look up table mayinclude two columns, a first column that may include a range of valuesof photosignals from the first detector array 110. In such a scenario,the second column could include values between 0.0 and 1.0 that mightrepresent the multiplier for the photosignals from the at least oneadditional photodetector 120.

In example embodiments involving the plurality of light sources 144, theoperations may include causing the plurality of light sources 144 toemit light into an external environment of the system so as to interactwith objects in the external environment to provide reflected light. Thelight detected from the shared field of view may include at least aportion of the reflected light. In such scenarios, the system 100includes at least a portion of a light detection and ranging (LIDAR)system. The LIDAR system may be configured to provide information (e.g.,point cloud data) about one or more objects (e.g., location, shape,etc.) in the external environment. While some described embodimentsinclude several light sources, other embodiments contemplated herein mayinclude a single light source.

In an example embodiment, the LIDAR system could provide point cloudinformation, object information, mapping information, or otherinformation to a vehicle. The vehicle could be a semi- orfully-automated vehicle. For instance, the vehicle could be aself-driving car or an autonomous drone, an autonomous truck, or anautonomous robot. Other types of vehicles are contemplated herein.

System 100 may include a communication interface 146. The communicationinterface 146 may be configured to provide a communication link betweenvarious elements of system 100 such as the controller 150, the pluralityof single-photon photodetectors 110, the at least one additionalphotodetector 120, the logic unit 130, one or more computing networks,and/or other vehicles.

The communication interface 146 could be, for example, a systemconfigured to provide wired or wireless communication between one ormore other vehicles, sensors, or other elements described herein, eitherdirectly or via a communication network. To this end, the communicationinterface 146 may include an antenna and a chipset for communicatingwith the other vehicles, sensors, servers, or other entities eitherdirectly or via the communication network. The chipset or communicationinterface 146 in general may be arranged to communicate according to oneor more types of wireless communication (e.g., protocols) such asBLUETOOTH, BLUETOOTH LOW ENERGY (BLE), communication protocols describedin IEEE 802.11 (including any IEEE 802.11 revisions), cellulartechnology (such as GSM, CDMA, UMTS, EV-DO, WiMAX, or LTE), ZIGBEE,dedicated short range communications (DSRC), and radio frequencyidentification (RFID) communications, among other possibilities. Thecommunication interface 146 may take other forms as well.

FIG. 1B illustrates a system 160, according to an example embodiment.System 160 may include some, or all, of the elements of system 100, asillustrated and described with reference to FIG. 1A. For example, system160 may include an emitter subsystem 170, which may include theplurality of light sources 144 and a light source controller 172. Theplurality of light sources 144 may be controlled by the light sourcecontroller 172.

System 160 also includes a receiver subsystem 180. The receiversubsystem 180 may include the plurality of single-photon photodetectors110 with the plurality of photodetectors of the first type 112 and theat least one additional photodetector 120 having one or morephotodetectors of the second type 122. Furthermore, the photodetectorsof the plurality of single-photon photodetectors 110 and the at leastone additional photodetector 120 could be coupled to the photodetectoroutput circuitry 128.

The receiver subsystem 180 also includes the logic unit 130. The logicunit 130 includes the first input channel 132 and the second inputchannel 134.

The emitter subsystem 170 and the receiver subsystem 180 may be coupledto the imaging optics 142. In such a scenario, the plurality of lightsources 144 may be configured to emit light pulses 162 into an externalenvironment 164 of the system 160. The light pulses 162 may interactwith objects in the external environment 164. For example, the lightpulses 162 may be reflected by the objects, at least in part, backtowards the receiver subsystem 180 as reflected light 166. The reflectedlight 166 may be received by the receiver subsystem 180 via the imagingoptics 142.

FIG. 1C illustrates a system 181, according to an example embodiment.System 181 may illustrate some elements, processes, or methods asillustrated and described with reference to FIGS. 1A, 1B, 2A, 2B, 3,and/or 4. For example, the plurality of single-photon photodetectors 110may provide plurality of single-photon photodetector signals 182. The atleast one additional photodetector 120 may provide at least oneadditional photodetector signal 184.

In an example embodiment, the single-photon photodetector signals 182and the at least one additional photodetector signal 184 may be inputinto the logic unit 130.

In such scenarios, the operations include forming a combinedphotodetector signal 190 based on a combination of the single-photonphotodetector signals 182 and the at least one additional photodetectorsignal 184. Furthermore, the logic unit 130 may be configured to receiveinformation indicative of an exposure condition 188. Yet further, thelogic unit 130 may be configured to receive information indicative of ahigh dynamic range profile 189. In such scenarios, forming the combinedphotodetector signal 190 could be based, at least in part on theexposure condition 188 and/or the high dynamic range profile 189.

FIG. 2A illustrates a system 200, according to an example embodiment.System 200 may include elements that are similar or identical to systems100 and 160 as illustrated and described with reference to FIGS. 1A and1B. The system 200 includes a first substrate 202 coupled to a secondsubstrate 204. The first substrate 202 may include a plurality ofsingle-photon photodetectors 210 and at least one additionalphotodetector 220. In such a scenario, the plurality of single-photonphotodetectors 210 may include a plurality of photodetectors of a firsttype 212. For example, the plurality of photodetectors of the first type212 could be disposed in a rectangular array along a first surface ofthe first substrate 202. Furthermore, the at least one additionalphotodetector 220 could include one or more photodetectors of a secondtype 222. For example, the one or more photodetectors of the second type222 could be disposed in a rectangular array along the first surface ofthe first substrate 202. That is, the respective types of photodetectorscould be disposed next to one another along a surface of the firstsubstrate 202.

In an example embodiment, the respective photodetectors of the pluralityof single-photon photodetectors 210 and the at least one additionalphotodetector 220 could be coupled to photodetector output circuitry 228(e.g., a readout integrated circuit (ROIC)) on the second substrate 204by way of respective arrays of through-wafer vias 223 and bump bonds229. Other types of electrically-conductive or wireless connections arecontemplated herein.

FIG. 2B illustrates a system 240, according to an example embodiment.System 240 may include elements that are similar or identical to systems100, 160, and/or 200 as illustrated and described with reference toFIGS. 1A, 1B, and 2A. In some example embodiments, system 240 mayinclude the plurality of single-photon photodetectors 210 being disposedas physically coupled to the at least one additional photodetector 220.As an example, the plurality of photodetectors of the first type 212 maybe stacked on the one or more photodetectors of the second type 222.Furthermore, in some embodiments, the photodetector output circuitry 228could be located on the first substrate 202. Other embodiments mayinclude the plurality of single-photon photodetectors 210 as beingdisposed in different orientations with respect to the at least oneadditional photodetector 220.

FIG. 3 illustrates a circuit 300, according to an example embodiment.Circuit 300 may be similar or identical to portions of systems 100, 160,181, 200, and/or 240 as illustrated and described in reference to FIGS.1A, 1B, 1C, 2A, and 2B. In an example embodiment, circuit 300 maydescribe a way for an amplifier chain to process one or both signalsfrom a given photodetector of the first type 312 and a correspondingphotodetector of the second type 322.

For example, the photodetector of the first type 312 may be connectedbetween a first reference voltage 330 and a first resistor 304. Thefirst resistor 304 may be connected to ground 320. Furthermore, circuit300 may include the photodetector of the second type 322, which may beconnected between a second reference voltage 332 and a second resistor314. The second resistor 314 may be connected to the ground 320.Additionally, a first capacitor 306 and a second capacitor 316 may beconnected between the output of their respective photodetectors and areference node 310. The voltage or current detected at the referencenode 310 could be output to a transimpedance amplifier (TIA) or anothertype of signal output.

In such a scenario, values of various components of circuit 300, such asthe resistors 304, 314 and capacitors 306, 316, may be adjusted and/orselected so as to adjust an output photosignal 334 that is provided tothe transimpedance amplifier. In other words, by selecting or adjustingthe component values, the first photosignal 318 and second photosignal324 may be mixed or otherwise combined to a desired degree prior toproviding the output photosignal 334. Such adjustment could additionallyor alternatively provide various frequency dependent behaviors. That is,a frequency response of the circuit 300 may be adjusted by changingcomponent values of the resistors 304, 314, and capacitors 306 and 316.

The RC filter (e.g., first resistor 304 and first capacitor 306)associated with the first photodetector 312 (e.g., a SiPM detector) maytune recovery time and ambient light response. The RC filter (e.g.,second resistor 314 and second capacitor 316) associated with the secondphotodetector 322 (e.g., an LmAPD detector) may be operable to tune arejection level of ambient or DC light sources. It will be understoodthat variations are possible based on this circuit arrangement. Forinstance, either of the first resistor 304 or the second resistor 314could be replaced by a regular diode to modulate photodetectorsaturation behavior. Furthermore, joint or individual biasing circuits(e.g., to provide first reference voltage V₁ 330 and second referencevoltage V₂ 332) could be added to further tailor the amplitude,duration, shape, and/or other aspects of the first photosignal 318, thesecond photosignal 324, and/or the output photosignal 334.

While circuit 300 illustrates one possible circuit configured to combinethe respective signals of the first photodetector 312 and the secondphotodetector 322, other circuits are possible. For example, therespective photodetectors 312 and 322 could have differentconfigurations, which may include respective amplifiers and outputs.

In some embodiments, circuit 300 may include a pole-zero configuration.For example, one or more resistors could be placed in parallel with thefirst capacitor 306 and/or the second capacitor 316.

In some embodiments, the SiPM and/or the LmAPD may be specifically sizedin terms of detector area. For example, one or more dimensions of theLmAPD may be selected so as to provide a desired high intensityresponse, which may be less strong than the small signal response due tothe SiPM.

Furthermore, the LmAPD dimensions may be selected so as to be smallenough that its noise does not approach or exceed the single photonresponse of the SiPM, which may lead to loss of sensitivity at smallsignals.

III. Example Methods

FIG. 4 illustrates a method 400, according to an example embodiment.Method 400 may be carried out, in full or in part, by system 100,controller 150, system 160, system 200, system 240, or circuit 300 asillustrated and described in reference to FIGS. 1A, 1B, 2A, 2B, and 3.Method 400 may include elements that are similar or identical to thoseillustrated and described with reference to FIGS. 1A, 1B, 2A, 2B, and 3.It will be understood that the method 400 may include fewer or moresteps or blocks than those expressly disclosed herein. Furthermore,respective steps or blocks of method 400 may be performed in any orderand each step or block may be performed one or more times.

Block 402 includes receiving a first photodetector signal from aplurality of single-photon photodetectors. The first photodetectorsignal is indicative of light from a field of view detected by thesingle-photon photodetectors.

Block 404 includes receiving a second photodetector signal from at leastone additional photodetector. The second photodetector signal isindicative of light from the field of view detected by the at least oneadditional photodetector. The plurality of single-photon photodetectorsincludes photodetectors of a first photodetector type. The at least oneadditional photodetector includes photodetectors of a secondphotodetector type (e.g., the at least one additional photodetector isother than a single-photon photodetector). The plurality ofsingle-photon photodetectors and the at least one additionalphotodetector are coupled to a substrate. In some embodiments, the firstphotodetector type includes silicon photomultiplier (SiPM) detectors.Additionally or alternatively, the second photodetector type couldinclude linear mode avalanche photodiode (APD) detectors.

As described elsewhere herein, some embodiments may include theplurality of single-photon photodetector and the at least one additionalphotodetector as being arranged on different substrates.

Block 406 includes selecting a photodetector signal from at least twoof: the first photodetector signal, the second photodetector signal, anda combined photodetector signal formed by combining the first and secondphotodetector signals.

Block 408 includes determining an intensity of light in the field ofview based on the selected photodetector signal. As an example,determining the intensity of light in the field of view could includedetermining at least a portion of a point cloud from a LIDAR device.

In some embodiments, selecting the photodetector signal may includecomparing the first photodetector signal to a first threshold. In suchscenarios, in response to a determination that the first photodetectorsignal is less than the first threshold, the method 400 may includeselecting the first photodetector signal as the selected photodetectorsignal.

Additionally or alternatively, selecting the photodetector signal mayinclude comparing the second photodetector signal to a second threshold.In such scenarios, in response to a determination that the secondphotodetector signal is greater than the second threshold, the method400 may include selecting the second photodetector signal as theselected photodetector signal.

In some embodiments, selecting the photodetector signal may includecomparing the first photodetector signal to a first threshold andcomparing the second photodetector signal to a second threshold. In suchscenarios, in response to a determination that the first photodetectorsignal is greater than the first threshold and the second photodetectorsignal is less than the second threshold, the method 400 may includecombining the first and second photodetector signals and selecting thecombined photodetector signal as the selected photodetector signal.

In some embodiments, combining the first and second photodetectorsignals may include adjusting the first photodetector signal. As anexample, adjusting the first photodetector signal may includemultiplying the first photodetector signal by a first value of a highdynamic range profile. Combining the first and second photodetectorsignals may also include adjusting the second photodetector signal. Suchadjustment of the second photodetector signal may include multiplyingthe second photodetector signal by a second value of the high dynamicrange profile. In such scenarios, combining the first and secondphotodetector signals may include summing the adjusted first and secondphotodetector signals.

As described elsewhere herein, the first photodetector type may include,without limitation, silicon photomultiplier (SiPM) detectors.Additionally or alternatively, the second photodetector type mayinclude, without limitation, avalanche photodiode (APD) detectors.

Optionally, method 400 may also include causing a plurality of lightsources to emit light into an external environment so as to interactwith objects in the external environment to provide reflected light. Insuch scenarios, the light detected from the shared field of view mayinclude at least a portion of the reflected light.

In some embodiments, method 400 may also include routing respectivephotodetector signals of the first photodetector array to a first inputchannel of a logic unit and routing respective photodetector signals ofthe at least one additional photodetector to a second input channel ofthe logic unit.

In some embodiments, method 400 also includes receiving informationindicative of an exposure condition of at least a portion of the sharedfield of view. In such scenarios, combining the first and secondphotodetector signals may be based on the received informationindicative of the exposure condition.

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anillustrative embodiment may include elements that are not illustrated inthe Figures.

A step or block that represents a processing of information cancorrespond to circuitry that can be configured to perform the specificlogical functions of a herein-described method or technique.Alternatively or additionally, a step or block that represents aprocessing of information can correspond to a module, a segment, aphysical computer (e.g., a field programmable gate array (FPGA) orapplication-specific integrated circuit (ASIC)), or a portion of programcode (including related data). The program code can include one or moreinstructions executable by a processor for implementing specific logicalfunctions or actions in the method or technique. The program code and/orrelated data can be stored on any type of computer readable medium suchas a storage device including a disk, hard drive, or other storagemedium.

The computer readable medium can also include non-transitory computerreadable media such as computer-readable media that store data for shortperiods of time like register memory, processor cache, and random accessmemory (RAM). The computer readable media can also includenon-transitory computer readable media that store program code and/ordata for longer periods of time. Thus, the computer readable media mayinclude secondary or persistent long term storage, like read only memory(ROM), optical or magnetic disks, compact-disc read only memory(CD-ROM), for example. The computer readable media can also be any othervolatile or non-volatile storage systems. A computer readable medium canbe considered a computer readable storage medium, for example, or atangible storage device.

While various examples and embodiments have been disclosed, otherexamples and embodiments will be apparent to those skilled in the art.The various disclosed examples and embodiments are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

What is claimed is:
 1. A system comprising: a substrate; a plurality ofsingle-photon photodetectors coupled to the substrate, wherein thesingle-photon photodetectors are arranged to detect light from a fieldof view; at least one additional photodetector coupled to the substrate,wherein the at least one additional photodetector is other than asingle-photon photodetector, wherein the at least one additionalphotodetector is arranged to detect light from the field of view; and acontroller configured to execute program instructions so as to carry outoperations, the operations comprising: receiving a first photodetectorsignal from the plurality of single-photon photodetectors, wherein thefirst photodetector signal is indicative of light from the field of viewdetected by the single-photon photodetectors; receiving a secondphotodetector signal from the at least one additional photodetector,wherein the second photodetector signal is indicative of light from thefield of view detected by the at least one additional photodetector;selecting a photodetector signal from at least two of: the firstphotodetector signal, the second photodetector signal, and a combinedphotodetector signal formed by combining the first and secondphotodetector signals; and determining an intensity of light in thefield of view based on the selected photodetector signal.
 2. The systemof claim 1, wherein selecting the photodetector signal comprises:comparing the first photodetector signal to a first threshold; and inresponse to a determination that the first photodetector signal is lessthan the first threshold, selecting the first photodetector signal asthe selected photodetector signal.
 3. The system of claim 1, whereinselecting the photodetector signal comprises: comparing the secondphotodetector signal to a second threshold; and in response to adetermination that the second photodetector signal is greater than thesecond threshold, selecting the second photodetector signal as theselected photodetector signal.
 4. The system of claim 1, whereinselecting the photodetector signal comprises: comparing the firstphotodetector signal to a first threshold; comparing the secondphotodetector signal to a second threshold; and in response to adetermination that the first photodetector signal is greater than thefirst threshold and the second photodetector signal is less than thesecond threshold, combining the first and second photodetector signalsand selecting the combined photodetector signal as the selectedphotodetector signal.
 5. The system of claim 4, wherein combining thefirst and second photodetector signals comprises: adjusting the firstphotodetector signal, wherein adjusting the first photodetector signalcomprises multiplying the first photodetector signal by a first value ofa high dynamic range profile; adjusting the second photodetector signal,wherein adjusting the second photodetector signal comprises multiplyingthe second photodetector signal by a second value of the high dynamicrange profile; and summing the adjusted first and second photodetectorsignals.
 6. The system of claim 5, wherein the high dynamic rangeprofile comprises a look up table, wherein the look up table comprisesvalues between 0.0 and 1.0.
 7. The system of claim 1, wherein theplurality of single-photon photodetectors comprises a siliconphotomultiplier (SiPM) detector, wherein the at least one additionalphotodetector comprises at least one of: an avalanche photodiode (APD)detector or a PIN photodiode detector.
 8. The system of claim 1, whereinthe substrate comprises a first surface, wherein the plurality ofsingle-photon photodetectors and the at least one additionalphotodetector are coupled to the first surface.
 9. The system of claim1, wherein the plurality of single-photon photodetectors is coupled toan upper surface of the at least one additional photodetector so as toform a stacked photodetector arrangement.
 10. The system of claim 1,wherein the substrate comprises a first surface along a primary plane,wherein at least a portion of detectors of the plurality ofsingle-photon photodetectors are arranged along the first surface amongat least a portion of detectors of the at least one additionalphotodetector so as to form an intermingled photodetector arrangement.11. The system of claim 1, further comprising imaging optics, whereinthe plurality of single-photon photodetectors and the at least oneadditional photodetector detect light from the shared field of view byway of the imaging optics.
 12. The system of claim 1, further comprisinga plurality of light sources, wherein the operations further comprisecausing the plurality of light sources to emit light into an externalenvironment of the system so as to interact with objects in the externalenvironment to provide reflected light, and wherein the light detectedfrom the shared field of view comprises at least a portion of thereflected light.
 13. The system of claim 12, wherein the systemcomprises at least a portion of a light detection and ranging (LIDAR)system, wherein the LIDAR system is configured to provide point cloudinformation to a vehicle.
 14. A method comprising, receiving a firstphotodetector signal from a plurality of single-photon photodetectors,wherein the first photodetector signal is indicative of light from afield of view detected by the single-photon photodetectors; receiving asecond photodetector signal from at least one additional photodetector,wherein the second photodetector signal is indicative of light from thefield of view detected by the at least one additional photodetector,wherein the at least one additional photodetector is other than asingle-photon photodetector, wherein the plurality of single-photonphotodetectors and the at least one additional photodetector are coupledto a substrate; selecting a photodetector signal from at least two of:the first photodetector signal, the second photodetector signal, and acombined photodetector signal formed by combining the first and secondphotodetector signals; and determining an intensity of light in thefield of view based on the selected photodetector signal.
 15. The methodof claim 14, wherein selecting the photodetector signal comprises:comparing the first photodetector signal to a first threshold; and inresponse to a determination that the first photodetector signal is lessthan the first threshold, selecting the first photodetector signal asthe selected photodetector signal.
 16. The method of claim 14, whereinselecting the photodetector signal comprises: comparing the secondphotodetector signal to a second threshold; and in response to adetermination that the second photodetector signal is greater than thesecond threshold, selecting the second photodetector signal as theselected photodetector signal.
 17. The method of claim 14, whereinselecting the photodetector signal comprises: comparing the firstphotodetector signal to a first threshold; comparing the secondphotodetector signal to a second threshold; and in response to adetermination that the first photodetector signal is greater than thefirst threshold and the second photodetector signal is less than thesecond threshold, combining the first and second photodetector signalsand selecting the combined photodetector signal as the selectedphotodetector signal.
 18. The method of claim 17, wherein combining thefirst and second photodetector signals comprises: adjusting the firstphotodetector signal, wherein adjusting the first photodetector signalcomprises multiplying the first photodetector signal by a first value ofa high dynamic range profile; adjusting the second photodetector signal,wherein adjusting the second photodetector signal comprises multiplyingthe second photodetector signal by a second value of the high dynamicrange profile; and summing the adjusted first and second photodetectorsignals.
 19. The method of claim 14, wherein the plurality ofsingle-photon photodetectors comprises silicon photomultiplier (SiPM)detectors, wherein the at least one additional photodetector comprisesavalanche photodiode (APD) detectors.
 20. The method of claim 14,further comprising causing a plurality of light sources to emit lightinto an external environment so as to interact with objects in theexternal environment to provide reflected light, and wherein the lightdetected from the shared field of view comprises at least a portion ofthe reflected light.